How to completely disable mobile data from being turned on?

I don't have a mobile data plan. We're waiting for my parents' contract to be up until we get a family plan. Anyways, mobile data keeps turning itself on for some reason and then AT&T keeps charging us $40 each month. And it's really annoying, as we're not rich (we got this phone off a family friend). Is there a way I could disable/keep it from being turned on any under circumstance unless I (the user) turn it on myself?

I don't have a mobile data plan. We're waiting for my parents' contract to be up until we get a family plan. Anyways, mobile data keeps turning itself on for some reason and then AT&T keeps charging us $40 each month. And it's really annoying, as we're not rich (we got this phone off a family friend). Is there a way I could disable/keep it from being turned on any under circumstance unless I (the user) turn it on myself?

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Try turning Airplane Mode on. That should kill all power to the radios. And unless AT&T didn't do anything stupid to the ROM, it should stay that way.

i have the same problem with galaxy S4, i have wifi connection at home and work but the automatically turning on of the data roaming is costing me, i have turned it off several time but it keeps coming on after a while, i should be able to do it manually but this thing keeps coming automatically

try this one.
go to settings, more networks, mobile network settings and deliberately edit the APN (access point name).
ex. choose a different authentication type and APN type.
save it and check by going to the browser if you can still connect to the internet.

I know that my answer is late, but I came across the same problem and I have solved it by:
going to settings > more connections > mobile networks > network mode
and there selecting the modes that don't have "(automatic connection)": "3G only" or "2G only".
Hope this helps other people that are in the same situation.